Two-way hybrid fiber-coaxial (HFC) networks are shared bi-directional networks with point-to-multipoint transmission in the downstream direction, and multipoint-to-point transmission in the upstream direction. Signals are distributed via a fiber optic connection from a head-end to a node that converts the optical signal to an electrical signal, and then distributes the signals to residences via a tree and branch coaxial cable distribution network. At the subscriber side, terminal equipment supports the delivery of cable services (video, data and voice services) to subscribers, via cable modems. Data and voice services are supported by cable modems and communication gateways, respectively, which require the use of an upstream signal path. The network uses a fiber optic upstream signal path from the node to the head-end. A return band is used to support transmissions from devices at subscribers' premises back to the head-end. In such networks, many cable modems may compete for communication bandwidth in both the upstream and downstream directions.
A cable modem generally uses standardized communication protocol based on the Data over Cable System Interface Specification (DOCSIS) to access data services through the cable network, by using the downstream path to indicate exactly when each modem is permitted to transmit in the upstream direction.
The DOCSIS utilizes two primary data transmission elements; (a) Cable Modem Termination System (CMTS) located in specified nodes on the HFC network for distributing data to end-of-line subscribers, and (b) a Cable Modem (CM) residing at subscriber's premise. Subscribers send data from their digital devices (PC, VoIP phone, Video IP device, etc) into the cable modem, which then relays the data to the CMTS, which in turn relays the information to the appropriate network element. Information destined to the subscriber digital device is provided from the network to the CMTS, which in turn relays the information to the CM. The CM in turn relays the information to the subscriber's digital device. Additional network elements may be placed inside the cable network to support service delivery or to monitor service quality. All system maintenance, operation and network communications are outlined in the DOCSIS specification.
The DOCSIS requires that the downstream communication path be properly functioning for any upstream communication to happen. In cases where the signal to noise ratio (SNR) is too low in the downstream path for the cable modem to receive data, the downstream path may be unusable while the upstream path may function correctly. In such cases, a service call may require a service technician to be dispatched to a subscriber's location, considerable cost and loss of time.
It is, therefore, advantageous to implement an overall network management system that can quickly and cost-effectively locate various network faults and monitor network performance to allow for optimum delivery of various services to subscribers.
Several attempts as outlined below have so far been made to provide solutions for remote end-of-line monitoring and automatically measuring and the signal quality of downstream communications and transmitting the measurements upstream without being dependent on the downstream channel to be fully functional.
U.S. Patent application No. 2004/0103442 by Eng discloses a system for end-of-line monitoring of a node with a network such as a DOCSIS network. The system of Eng comprises a CMTS including a status monitoring Media Access Control (MAC), a network manager coupled to the CMTS, and status monitoring cable modems at termination points. The status monitoring cable modems include a measuring device capable of detecting and measuring downstream communication signals in the DOCSIS network and a transmitter for transmitting status information over the network to the status monitoring MAC at the CMTS. The measuring device is capable of measuring signal to noise ratio, power level, or other performance measurements. The status monitoring cable modem collects the status information from the measuring device and the transmitter transmits status packages over the network to the status monitoring MAC utilizing a special service channel. The status packages are transmitted at random intervals or only when a problem exists. The status monitoring MAC receives and decodes the status packages and relays the status information to the network manager. The network manager processes the status information and provides diagnostic, alerting, and other information to service personnel. Hence, Eng implements status monitoring and signal measuring capabilities into standard cable modems that are capable of utilizing the existing DOCSIS network for transmitting status information to the head-end equipment for evaluation. In this approach, however, the cable modem not being a stand-alone device would need to be powered from a source other than the communication trunk, which may impose certain practical limitations. Furthermore, in order to implement such a system, standard cable modems would have to be replaced at all termination points with cable modems incorporating the components for performing the status monitoring as disclosed above, which would incur a considerable additional system cost.
We also note that U.S. Patent application No.2004/0073664 by Bestermann and U.S. Pat. No. 6,393,478 issued to Bahlmann disclose alternative systems in which a cable modem is utilized to transmit status information to another device for analysis over the network. In Bestermann's system, the cable modem includes server software 20 that communicates with client software 24 through the CMTS 8 at the head-end. The server software 20 delivers measurement data stored in buffer 16 of the cable modem 6. This communication is performed using the IP protocol. This method of data communication is used to provide the data to a remote device rather than requiring a portable diagnostic device 12 to be coupled to port 14 to receive performance data as they are provided to port 14. Bestermann's system enables the network operator to avoid sending technicians for diagnostic visits and the proprietary implementation of such portable devices. Again, these two systems would require the cable modems to be modified to incorporate the software for communicating with the remote diagnostic device, involving a considerable additional cost.
U.S. Patent application No 2005/0047442 A1 by Volpe et al. describes an apparatus for quantifying and measuring communication signals in a HFC DOCSIS network. However, this apparatus does not take advantage of the DOCSIS standard for communicating the measurements or status information are over the DOCSIS network.
U.S. Pat. No. 6,802,032 issued to Budinger et al., U.S. Pat. No. 6,785,292 issued to Vogel, and U.S. Pat. No. 6,711,135 issued to Dziekan et al. and U.S. Patent application No. 2004/0037217 by Danzig et al. describe various systems for monitoring and performing diagnostics of communication signals in a CMTS or DOCSIS network. Again the systems disclosed in these references would require devices which are not stand-alone, thereby would need to be powered from a source other than the communication trunk, which may impose certain practical limitations.
In view of the limitations in the prior art reviewed above, there still remains a clear need for a stand-alone network monitoring apparatus, that is capable of being operated at any point in the HFC network and powered directly from the communication trunk, and without necessitating a replacement or modification of any of the existing network equipment.
An object of the present invention is to provide an economical stand-alone network monitoring apparatus to be powered directly from the communication trunk, that is capable of being operated at any point in the HFC and communicating over the DOCSIS standard while concurrently making uninterrupted real-time measurements of the HFC network performance in terms of physical layer parameters. A further object of the present invention is to provide a stand-alone network monitoring system that is capable of recording performance over a period of time to find intermittent problems that plague some cable systems.